Production of phosphoric esters of aliphatic alcohols



Patented June 24, 1930 UNITED STATES PATENT OFFICE FRITZ NIOOLAI, OF LUDWIGSHAFEN-ON-THE-BHINE, GERMANY, ASSIGHOR '10 I. G. FARBENINDUSTRIE AKTIENGESELLSCHAFT, OF FRANKFORT-ON-THE-MAIN, GER- MANY, A. CORPORATION 01 GERMANY PRODUCTION OF PHOSPHORIC ESTERS OF ALIPHATIG ALOOHOLS flo m'awing. Original application filed September 4, 1928, Serial No. 303,855, and in Germany October 18, 1927. Divided and this application filed September 4, 1929. Serial No. 380,427.

The present invention relates to the production of phosphoric esters of aliphatic alcohols.

The neutral phosphoric esters of aliphatic 6 alcohols have hitherto been prepared either from silver phosphate and alkyl iodides, or by the action of phosphorus oxychloride on sodium alcoholates. Although it has already been proposed to produce triethyl phosphate by the action of phosphorus oxychloride on anhydrous ethyl alcohol, it was considered necessary in this case to cool strongly with ice, in order to prevent the evolution of the hydrochloric acid during the reaction, the hydrochloric acid being thereupon displaced from the resulting mixture by a continuous current of dry carbon dioxide, and the mixture being gently warmed on the water bath. This method of working however is not applicable for industrial purposes, since the yield of triethyl phosphate is insufiicient, whilst the conditions change even more for the worse if other alcohols be employed.

1 have now found that neutral phosphoric esters of primary aliphatic alcohols are obtained, with good, and in many cases nearly quantitative, yields by allowing phosphorus oxychloride to act on the alcohols in such a way that the hydrochloric acid formed during the reaction is removed as such from the reaction liquid while the reaction is still proceeding. This can be effected by working at elevated temperatures, preferably at about the boilingpoint of the mixture, or by carrying on the reaction under reduced pressure,

the combination of both conditions being particularly advantageous.

For example, the process may be carried out by placing the alcohol in a vessel connected with a reflux condenser and under reduced pressure, and warming itto the desired temperature, the phosphorus oxychloride being then gradually admitted, in liquid or vapor form, whilst the bulk of the hydrochloric acid formed is continuously removed. The mixture is then kept boiling for a short time, under reduced pressure, until the vapors of hydrochloric acid have almost entirely passed over, the resulting trialkyl phosphate being afterwards recovered by distillation under reduced pressure. It is advantageous to employ an amount of alcohol in excess to that required for esterification, but other suitable diluents may also be added, preferably such as lower the boiling omt of the mixture, such as chloroform or enzene. Moreover, metallic catalysts, such as copper powder, metal chlorides, and the hke may be added to the reaction liquid, in order to facilitate the splitting 011' of the hydrochloric acid. The degree of reduced pressure employed may vary within wide limits, but should be as low as attainable. If desired, the components may also be mixed in the cold, and the reaction then carried to completion by heating, reduced pressure hemg employed, for example by passing the peiction mixture through a heated vessel or The following examples will further illustrate the nature of the said invention which however is not restricted thereto. The parts are by weight.

E wample 1 The vapors of 154 parts of phosphorus oxychloride under an absolute pressure of 25 to 40 millimeters of mercury, are passed 1n the course of 30 minutes into 400 parts of n-butyl alcohol at about C., contained in a vessel provided with a reflux condenser. The mixture is then kept boiling for from about 30 to minutes longer, and, subsequently, the remainders of butyl alcohol are distilled ofi', followed by the resulting tributyl phosphate, by distillation under a good vacuum. Pure tri-n-butyl phosphate boils at 135 C. under a pressure of 5 millimeters of mercury. The yield is about 85 per cent of the theoretical.

If, under the same conditions, the n-butyl alcohol be replaced by isobutyl alcohol or primary amyl alcohol, the latter for example in the form of fermentation amyl alcohol, a similarly good yield is obtained of tri-isobutyl phosphate, boiling at 112 C. under 4 to 5 millimeters of mercury, or tri-amyl The procedure is similar for the production of triethyl phosphate.

E mample 52 By working with the same amounts of phosphorus oxychloride and isobutyl alcohol as specified in Example '1, but under atmospheric pressure and at a temperature of from to C., tri-isobutyl phosphate is also obtained, but in a smaller yield than when operating under reduced pressure, namely about 7 0 per cent of that obtained according to Example 1.

This application has been divided out from my copending application for patent, Ser. N 0. 303,955, filed Septemer 4, 1928.

What I claim is 1. As new articles of manufacture neutral phosphoric esters of aliphatic alcohols containing more than 4 carbon atoms in the molecule.

2. As a new article of manufacture triamyl phosphate boiling at about 143.5 C. under a pressure of 2.5 millimeters (mercury e 3. The process of producing neutral phosphoric esters of primary aliphatic alcohols which comprises acting with phosphorus oxychloride upon a primary aliphatic alcohol containin more than four carbon atoms in its molecu e, while heating and continuously removing the hydrochloric acid formed during the process.

In testimony whereof I afiix my signature.

FRITZ NICOLAI. 

